Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the actuator arm as it seeks from track to track.
An air bearing forms between the head and the disk due to the disk rotating at high speeds. Since the quality of the write/read signal depends on the fly height of the head, conventional heads (e.g., magnetoresistive heads) may comprise a fly height actuator (FHA) for controlling the fly height. Any suitable FHA may be employed, such as a heater which controls fly height through thermal expansion, or a piezoelectric (PZT) actuator. It is desirable to determine the appropriate setting for the FHA control signal (e.g., appropriate current applied to a heater) that achieves the target fly height for the head.